Previously, in U.S. Pat. No. 5,370,315, the present inventors addressed the problem associated with spraying materials that required continuous circulation. The present invention addresses the problems associated with spraying materials that contain a significant particulate content, but do not require continuous circulation.
When spraying liquids, a liquid and compressed air are mixed in a mixing chamber to atomize the liquid before the mixture exits out a discharge orifice. To provide a proper spray pattern, the liquid must be sufficiently atomized. When using conventional liquids that do not contain a significant particulate content, such as paint, the pressure of the air supplied to the mixing chamber can simply be increased to ensure proper atomization.
When spraying liquids containing a high particulate content, increasing the air pressure has adverse effects. When spraying such liquids on vertical or overhead surfaces, the particles in the mixture tends to bounce off the surface to which the mixture is being applied, instead of adhering to the surface with the liquid. As the pressure of the air supplied to the mixing chamber is increased, the tendency of the particles to bounce off the surface increases.
Proper atomization of the liquid sprayed and proper adhesion of the particles in the liquid,are conflicting problems that are well known. However, conventional spray devices have been unsatisfactory in resolving these problems.
In addition to these problems, when spraying liquids having a high particulate content, the air passages that lead to the mixing chamber must be sufficiently large to introduce an adequate supply of pressurized air for proper atomization of the liquid. At the same time, increasing the size of the air passages increases the amount of material that may flow back through the air passage instead of exiting through the discharge orifice. When using a liquid with high particulate content, this back flow can significantly occlude the air passage, hindering the performance of the spraying apparatus.
Finally, it is beneficial to be able to remove the nozzle periodically during use so that the nozzle can be cleaned or replaced. If the spray device does not provide an adequate seal, the spray materials will have to be depressurized before removing the nozzle. Otherwise spray material would leak through the spray device.
Depressurizing the spray materials wastes significant time because the materials must also be repressurized once the nozzle is replaced. To provide an adequate seal, previous devices have used a resilient sealing component. Such components tend to wear and require replacement, especially if materials having a significant particulate content are used. Therefore, it is advantageous to create a durable seal that does not require replacement.